The present invention relates generally to a navigation system for a vehicle and method therefor. More particularly, the present invention relates to navigation systems and methods employing a graphic display unit on which a roadmap and the current position of the vehicle are displayed, so that the driver of the vehicle can drive the vehicle in accordance with a preset travel course displayed on the display unit.
This kind of navigation system for vehicles is disclosed in a Japanese Patent Application Unexamined Open No. Sho. 58-150814, published on Sept. 7, 1983. In this Japanese Patent Application document, data, specifically main passage points such as intersection, specifying a route of travel from a start point to a destination are entered and stored with reference to the displayed roadmap. Whenever the vehicle approaches one of these main passage points, the navigation system detects the approach of the main passage point and displays information such as messages to "turn left" or "go straight", indicating passage of the main passage point, and arrival at the destination, so that the driver can more easily reach the destination with the guidance of the navigation system.
However, the conventional navigation system has the problem described below. Guidance along the course of travel is generally initiated in response to a command to start the guidance process at a registered intersection designated as the starting point of the set route of travel Thus, if the vehicle should fail to pass through the registered intersection at which the route should have started or if the driver should fail to give the command to start the guidance process when the vehicle returns the first intersection, the driver must take the trouble of returning to that intersection or point in order to properly start the guidance process. Consequently, there is occasionally some inconvenience in starting on the selected course of travel.